This application corresponds to German Application No. 100 55 262.5 filed Nov. 8, 2000, herein incorporated by reference in its entirety.
1. Field of the Invention
This invention relates generally to axial piston machines and, more particularly, to a hydrostatic axial piston machine having a cylinder block in which there are bores to hold reciprocating pistons, and with a swashplate on which the reciprocating pistons are supported and in which there are control ports to supply the bores with hydraulic medium.
2. Technical Considerations
DE 196 42 022 A1 describes an axial piston machine. The field of application of the machine disclosed therein, with a control system and hydraulic fluid supply system in the swashplate, is limited because the intake and delivery volume is constant.
It is an object of the present invention to provide an axial piston machine of the general type described above but with an expanded range of potential applications.
The invention provides an axial piston machine in which the swashplate is adjustable. It thereby becomes possible to increase the transformation range of a hydrostatic transmission in which the axial piston machine of the invention is used by regulating not only the primary side (i.e., adjustment of the delivery volume of the pump) but also the secondary side (i.e., adjustment of the intake volume of the motor).
In one advantageous configuration of the invention, the swashplate includes a pivoting cradle mounted in friction bearings in a cradle receptacle. Hydraulic fluid channels empty into the cradle receptacle and, regardless of the rotational position of the cradle, are in connection with feed channels in the cradle that are connected to control ports. The bores in the cylinder block are, therefore, supplied with hydraulic fluid via the adjustable cradle. As a result of the hydraulic fluid channels that emerge in the cradle receptacle, the friction bearing system of the cradle can also be pressurized with hydraulic fluid to achieve a hydrostatic relief of the cradle.
Pivot means can be provided to pivot the cradle. The pivot means can comprise an actuator piston that is oriented substantially perpendicular to the axis of rotation of the cylinder block and substantially perpendicular to the axis of rotation of the cradle and that is actively connected with the cradle. If the actuator piston has a toothed rack segment that engages a toothed segment on the back side of the cradle, there is a constructively simple and functionally reliable active connection between the actuator piston and the cradle in which the actuator piston is tangentially engaged with the back side of the cradle.
The invention teaches that it is appropriate if the actuator piston is located between two friction bearing segments of the cradle receptacle and is centered with respect to the cradle.
The cylinder block advantageously has an external bearing system. An external bearing system minimizes the dimensions of the axial piston machine of the invention in the radial direction. In this case, it is advantageous if the cylinder block bearing system has two helical roller bearings in an O-arrangement.
In one particularly advantageous configuration of the invention, the axial piston machine is configured as a hub drive, in particular a wheel hub drive, whereby the cylinder block forms a rotating hub, a housing that surrounds the cylinder block serves as the hub carrier, and the cylinder block bearing system is realized in the form of a hub bearing system. The cylinder block can include a wheel fastening flange and a rim centering device.
In an additional advantageous configuration of the invention, a brake is connected between the cylinder block and the housing. The brake can be a wet-running, hydraulically-relieved, spring-loaded, multiple-disc brake. In this case, the brake can be cooled by hydraulic fluid, as a result of which it can absorb a high braking power.